The natural course of induced myocardial ischemia in conscious unsedated pigs will be determined with regard to regional blood flow and contractile function. Pigs will be studied because no significant pre-exisiting collateral vessels occur making this model analogous to man. The primary objectives of this study are: (1) to determine the temporal correlation of regional myocardial blood flow, mechanics and work index, (pressure-length loop area) during the natural development of collateral vessels; (2) to evaluate the salutary potential of nitrogylcerin and propranolol in modifying these relationships; and (3) to characterize the regional myocardial responses to cessation of the pharmacologic interventions. Domestic swine (35-45 kg) will be anesthetized with halothane and instrumented with catheters in aortic arch, left atrium and coronary sinus for pressure (p), microsphere flow determination and cardiac output; a miniature solid state transducer in the left ventricle (LV) for LVP and dp/dt; multiple pairs of ultrasonic length transducers in normal, border and ischemic myocardial zones for segment length (SL) and velocity of shortening, dSL/dt; and a teflon snare around the distal left anterior descending coronary artery for production of regional LV ischemia. Studies will begin 5 to 7 days after operation when pigs are vigorous and healthy. The basic protocol is: a 4 day sequence with pharmacologic intervention from 2 hours after occlusion until 24 hours followed by a 3 day period with no intervention administered during which the regional cardiac responses to drug cessation will be assessed. Thus, simultaneous and sequential analysis of the relation of regional myocardial blood flow and mechanical function in the same location, and the modification of the relation by pharmacologic agents in a clinically relevant animal model will be obtained by mutually independent techniques.